A biosensor may be denoted as a device that may be used for the detection of an analyte that combines a biological component with a physicochemical or physical detector component.
For instance, a biosensor may be based on the phenomenon that capture molecules immobilized on a surface of a biosensor may selectively hybridize with target molecules in a fluidic sample, for instance when an antibody-binding fragment of an antibody or the sequence of a DNA single strand as a capture molecule fits to a corresponding sequence or structure of a target molecule. When such hybridization or sensor events occur at the sensor surface, this may change the electrical or optical properties of the surface that can be detected as the sensor event.
US 2003/0174923 discloses detecting and/or measuring a substance based on a resonance shift of photons orbiting within a microsphere of a sensor. Since the resonance of the microsphere has a large quality factor, the sensor is sensitive. The sensor includes the microsphere coupled with at least one optical fiber. The surface of the microsphere includes receptors complementary to the substance. The at least one optical fiber can be provided with at least one additional microsphere having a surface free of the receptors. Resonance shifts observed in such an additional microsphere(s) can be attributed to factors unrelated to the presence of the substance. The resonance shift observed in the microsphere with the receptors can be compensated based on the resonance shift of the additional microsphere(s) to remove the influence of these other factors.
Vollmer et al. (2003), “Multiplexed DNA Quantification by Spectroscopic Shift of Two Microsphere Cavities”, Biophysical Journal, Volume 85, pp. 1974-1979 discloses a spectroscopic technique for high-sensitivity, label-free DNA quantification. An optical resonance (whispering gallery mode) excited in a micron-sized silica sphere can be used to detect and measure nucleic acids. The surface of the silica sphere is chemically modified with oligonucleotides. Hybridization to the target DNA leads to a red shift of the optical resonance wavelength. Furthermore, each microsphere can be identified by its unique resonance wavelength. DNA detection is demonstrated by using two microspheres. The multiplexed signal from two microspheres allows to discriminate a single nucleotide mismatch in an 11-mer oligonucleotide with a high signal-to-noise ratio of 54. This all-photonic whispering gallery mode biosensor can be integrated on a semiconductor chip that makes it an easy to manufacture, analytic component for a portable, robust lab-on-a-chip device.
Conventional biosensor chips based on whispering gallery modes may require a measurement that takes a comparatively long amount of time.